Does prefabrication make green houses more affordable? BuildingGreen associate editor Allyson Wendt asked this question in 2007 when she was working on a feature article on the topic. Back then, the answer was “not quite yet.” Here’s what she has to say today.

More than a year later, the answer still seems to be “not quite yet,” at least according to Chad Ludeman, developer of the 100K house in Philadelphia, in an article on the green building blog, www.jetsongreen.com.

He argues that most of the modernist houses could be site-built for less money; that overengineering in the prefab industry makes the less-waste argument specious; that long waiting lists for prefab homes make time savings irrelevant; and the green aspects of prefab rest largely on the “no waste” element.

Ludeman’s arguments are good ones, especially as the majority of the industry stands right now. If green features—superinsulation, benign materials and finishes, and energy- and water-efficient appliances and fixtures—aren’t standard, prefabrication doesn’t offer many cost benefits over site-built homes, since prefabrication depends on volume to realize its claimed benefits. Most companies producing modernist, green, or modernist-green prefabs are still small and don’t yet have enough volume to significantly lower material and labor costs. For larger companies, green features mean modifications to their stock plans, which means extra expense.

Ludeman suggests a semi-custom approach with prefabricated components and custom, local finishing—an approach many production builders already use for large developments. Adjusting this approach for infill development would be a great idea. There are several companies out there that mix and match prefabricated components in custom and semi-custom structures.

However, environmentally speaking, the jury is still out, and the potential benefits of prefab green (worker transportation, site impacts, etc.) go far beyond the waste reductions.

Unlike Ludeman, I’m not ready to give up on prefabrication just yet. I still think there’s promise in the idea of prefabricated green, especially in the mainstream and affordable housing markets. As for green modernist housing, the benefits of prefabrication may never come through for such a relatively small market.

As an industry insider in the modular home business, Blu Homes‘ Maura McCarthy says she agrees that conventional prefab companies are not outperforming site-built homes. But, she points out, smart prefab companies have the opportunity to do a lot better.

“If you take the scale efficiencies of manufactured homes, and introduce products like spray foam insulation,” says McCarthy, “all of a sudden you are providing spray foam at half the cost of spray foam provided on-site by a skilled subcontractor. This kind of ‘scale’ logic also holds true for a number of other functions, like the fabrication of countertops made of new, green materials, prefab components like kitchen/bath/utility pods, etc. Moreover, prefab companies have more possibility for innovation given their indoor facilities and opportunity to do research on new technologies.”

As for the waste issue, she fully disagrees that the waste in prefab building is comparable to that for site-built homes. “My experience is that most prefab companies produce at least 50% less waste than normal construction. And although you can certainly hire someone to come and haul away the huge garbage bins of waste that you see at every single site-built construction site, the amount of waste in factory versus site-built homes is just not comparable. There are a host of reasons for this, including precise volume purchasing by factories, better storage areas (i.e., not out in the rain) that keep materials protected, and so on. Prefab manufacturers may have gotten a few things wrong, but less waste is not one of them in my opinion.”

She thinks that Ludeman makes many of the right points and criticisms of existing prefab companies, but believes these criticisms are of a very nascent industry—that is, the modern prefab homes industry—which needs to break away from its older brother, the modular homes industry.

“With a new U.S. administration that values ‘greener’ technologies, American consumers who are not only much better educated on the carbon footprint of their homes, but more demanding about the convenience with which their homes are delivered, coupled with the current housing crisis that is wiping out many of the low performers,” says McCarthy, “the macro trends toward more green prefab seem positive.”